The overall objective of this research is to examine pulmonary cell renewal as related to tissue injury and repair. Three areas of study are being pursued. In the first, we are determining whether the proliferative response following injury is a quantitative measure of the amount of injury. To do this, we are correlating the proliferative response with morphometric measurements of the amount of tissue damage after exposure to NO2. In the second area, we are testing the ability of dietary vitamin E and selenium to alter the amount of lung damage. To assess this, we are quantitating the amount of injury following exposure to NO2 of rats on diets supplemented with and deficient in these antioxidants. In the third area, we will determine whether tolerance in the epithelium of rats exposed to NO2 is associated with increased turnover or accumulation of cells. This will be accomplished by measuring the proliferative response and differentiation of Type 2 cells to Type 1 cells and nonciliated bronchiolar cells to ciliated cells in the epithelium tolerant to NO2.